In places were a "dive flag" is required a ball or float might not pass muster with the marine police.
I dive in areas with docks and made a dive float from a fishing float I picked up at West Marine, an old folding tent pole running up thru it, flag on top and a few fishing sinkers I found clamped to the bottom to keep it upright.
It’s just buoyant enough to float but I can pull it under to go under docks or make it bob when I hear a boat too close so they can see there is really a diver down.